1. Field of the Invention
The invention relates to a ribbon cassette for a typewriter or the like, comprising a housing, a take-off spool core rotatably seated in the housing, on which a take-off ribbon spool is wound, and a take-up spool core, also rotatably seated in the housing, where at least the take-off spool core is rotatably seated in the housing vertically to its axis of rotation, and where a loop brake spring with two legs and with a section in the shape of a segment of a circle connecting the legs and looping around the take-off spool core is provided.
It is intended by means of the movable seating of the takeoff spool core provided in such cassettes to take up a space corresponding to less than twice the diameter of the take-off spool, and to allow the axis of rotation of the take-off spool to come closer to the housing wall, so that the space available for the take-up spool, the diameter of which grows larger, is increased.
2. Description of Prior Art
It is known in the prior art to provide for such ribbon cassettes a brake spring for the take-off spool in order to prevent an undefined unwinding process because of vibrations during operation or transport, as well as to maintain defined ribbon tension.
To keep the ribbon tension constant, while the diameter of the take-off spool is decreasing, it is necessary that the braking force be reduced in the course of the typing process, i.e. with increasing use of the ribbon.
To achieve this it is known, for example from German Utility Model DE-GM 89 09 019, to roughen or abrade the spring in the area where it rests against the take-off spool core, so that the take-off spool core is ground down by the spring in the course of operation and the effective diameter is reduced in this way, which is also coupled with a progressively reduced brake effect.
It is known from German Letters Patent DE-PS 25 52 154 to provide brake elements, in contact with the take-off spool and extending radially over the ribbon, which exert a frictional brake force on the unwound ribbon, the effective friction surface of these brake elements changing in a radial direction, so that the brake force changes too as a function of the still available amount of ribbon or the diameter of the take-off spool.
Both known solutions have the disadvantage that, although the fictional forces are to be correctly altered in intent, a defined setting of the ribbon tension independently of outside influence, such as temperature and humidity and the like, cannot be sufficiently assured.